1. Field of the Invention
This invention relates to a sound effect-creating device for electronic musical instruments and the like, and more particularly to a sound effect-creating device for adding a reverberation signal to a monaural original tone signal, delaying the resulting monaural reverberation tone signal by respective desired time periods by means of a plurality of delay circuits selected by a player or operator, and combining the resulting delayed monaural reverberation tone signals as desired, to impart a reverberation effect for creating impressions of a spread of a sound and the like to the monaural original tone signal.
2. Prior Art
In electronic musical instruments, such as electronic pianos and other electronic keyboard instruments, an artificial musical tone in an audio frequency range, which corresponds to a key of the keyboard selectively depressed by a player, is synthesized by electronic computation. In such electronic synthesis, the artificial musical tone is not only synthesized in a desired tone color and tone quality, but also often imparted with various sound effects produced according to settings selectively made for control thereof by the player via switches, volume knobs, and the like of the instrument. The sound effect includes a reverberation which additionally creates an impression of a spread of a sound on listeners. This effect of reverberation makes the listeners feel as if they were listening to a player playing the electronic instrument in a concert hall. Therefore, in the field of the electronic musical instruments, how to create the impression of a spread of a sound and the like is a very important technique in designing an instrument.
FIG. 1 shows a conventional sound effect-creating device of this kind. The sound effect-creating device, generally designated by reference numeral 81, comprises a monaural original tone signal-mixing circuit 82, a reverberation circuit 83, a delay circuit 84, mixing circuits 85, 86, and amplitude control circuits 87 to 94.
The monaural original tone signal-mixing circuit 82 adds up stereophonic original tone signals to form a monaural original tone signal. The circuit 82 has input terminals 82a, 82b connected, via the amplitude control circuits 87, 88 for controlling the amplitudes (or volumes) of stereophonic original tone signals, to a left channel 95 and a right channel 96, respectively. It also has an output terminal 82c connected to an input terminal of the reverberation circuit 83.
The reverberation circuit 83 adds a reverberation tone signal to the monaural original tone signal to form a monaural reverberation tone signal. This circuit 83 has an output block which bifurcates into Paths, one of which is connected via an amplitude control circuit 89 to an input terminal of the delay circuit 84, and the other of which is connected via an amplitude control circuit 90 to input terminals of respective amplitude control circuits 92, 94. The delay circuit 84 delays the monaural reverberation tone signal by a predetermined time period, and has an output terminal connected to input terminals of respective amplitude control circuits 91, 93.
The mixing circuits 85, 86 add up the delayed monaural reverberation tone signal and the monaural reverberation tone signal to form stereophonic signals, which are delivered to the left and right channels 97, 98, respectively. The mixing circuit 85 has input terminals connected to output terminals of the amplitude control circuits 91, 92, and an output terminal connected to the left channel 97, while the mixing circuit 86 has input terminals connected to output terminals of respective amplitude control circuits 93, 94, and an output terminal connected to the right channel 98.
The left and right channels 97, 98 are connected via arithmetic circuits, digital-to-analog converters, and audio amplifiers, to left and right loudspeakers, neither of which are shown, respectively.
The sound effect-creating device 81 adds up the stereophonic original tone signals to form the monaural original tone signal, and then adds the reverberation tone signal to the monaural original tone signal, to form the monaural reverberation tone signal. The monaural reverberation tone signal and the delayed monaural reverberation signal are each supplied to bifurcated paths, and controlled to predetermined amplitudes by the respective amplitude circuits to form four signals. These signals, are added up in selected combinations thereof to form stereophonic tone signals which are capable of creating an impression of a spread of a sound. This method is based on the principle that when an original signal is delayed 50 to 100 msec., a tone produced by the resulting delayed signal can be timewise separated from a tone produced by the original signal.
More specifically, according to the sound effect-creating device 81, the amplitude control circuits 87, 88 control the stereophonic signals input from the left and right channels 95, 96 to predetermined amplitudes, and the resulting signals are added up by the monaural original tone signal-mixing circuit 82 to form the monaural original tone signal. Then, the reverberation circuit 83 adds the reverberation tone signal having predetermined delay times to the monaural original tone signal, to form the monaural reverberation tone signal. The monaural reverberation tone signal is supplied into bifurcated paths, one of which is connected to the amplitude control circuit 89, where the signal is controlled to a predetermined amplitude, and then delivered to the delay circuit 84, and the other of which is connected to the amplitude control circuit 90, where the signal is controlled to a predetermined amplitude, and then further supplied to bifurcated paths connected to the amplitude control circuits 92, 94, where the signals transmitted via the bifurcated paths are controlled to predetermined amplitudes. The resulting signals controlled with respect to their amplitude are input to the mixing circuits 85, 86, respectively.
The delayed monaural reverberation tone signal output from the delay circuit 84 is supplied into bifurcated paths, one of which is connected to the amplitude control circuits 91, 93, where the signal is controlled to respective predetermined amplitudes, and then the resulting signals having controlled amplitudes are supplied to the mixing circuits 85, 86, respectively.
The mixing circuits 85, 86 add up combinations of the delayed monaural reverberation tone signals and the monaural reverberation tone signals, to deliver the resulting signals to the left and right channels 97, 98.
By virtue of the above process, the delayed monaural reverberation tone signals are timewise separated from the monaural reverberation tone signals, and have different characteristics from those of the monaural reverberation tone signals. A selected combination of these two kinds of signals are added up, and then delivered to the left and right channels 97, 98. The signals are then supplied via the digital-to-analog converters, etc., to the left and right loudspeakers, not shown, realizing a stereophonic sound which creates an impression of a wider spread of sound than the stereophonic original sound.
However, such a conventional sound effect-creating device suffers from the following problems: By nature, stereophonic sounds echo back in various manners in an architecture, and the spread of a sound varies with the lapse of time. However, tile conventional device can only impart a rather simple reverberation to the original sound. That is, according to this device, the stereophonic original tone signals are added up, and then reverberation tone signal is simply added to the resulting monaural signal, followed by preparing the timewise separated signal therefrom, and adding up the monaural reverberation signals and the timewise separated signals controlled in amplitude in selected combinations, to impart to the original sound the effect of creating the impression of a spread of a sound on listeners. Therefore, a sound image resulting from the monaural reverberation tone signals is localized at a position determined by the amplitudes of the monaural reverberation tone signals delivered to the left and right channels, respectively. Then, after the lapse of the delay time; the sound image is shifted to a position determined by the amplitudes of the delayed monaural reverberation tone signals. Therefore, the localization of the sound image changes in a relatively simple manner, and hence it is impossible to create the effect of a sufficient spread of a sound which varies with the lapse of time. Further, the device can only provide a combination of the monaural reverberation tones and the delayed monaural reverberation tones, so that variation in reverberation of the sound obtained thereby is not sufficient.
Further, the components of the sound produced from the left and right loudspeakers connected via the audio amplifiers to the left and right channels are only two kinds, i.e. the monaural reverberation tone and the delayed monaural reverberation tone, and hence there is not sufficient thickness of the sound.